I read this and I realized I said look at the histogram, but I just assumed you knew what to look for. :) For good exposure, you usually want your peaks nicely distributed around the center area of the histogram. What you want to almost always avoid is cutoff. Where the histogram is shoved up against the left or right side. If you have an empty gap to the left and right sides then you know you've captured all of the information available and if need be can at least fix it in Photoshop if necessary. For low key, you'll of course want most of the distribution from your mids (center) to the shadows (left side) and the reverse for high key (mids to highlights). But there is no real rule, you have to think about the composition and lights/darks in a shot and know beforehand kind of how the histogram "should" look. The thing to remember in your case is if you look at your shot on the LCD and it looks ok and you then look at the histogram and everything is jammed over to the left then it's most likely underexposed. If it's jammed all the way to the right it's overexposed (of course, if you have it set, the 10D should be flashing all of the blown-out highlights at you in bright red anyway). That make any sense? -=>Donald